ROAMING OF THE FLY 



88 



make long excursions from it, perhaps in search of food 

 or breeding places, and may be found in places where 

 there is practically no shade and where it could not abide 

 permanently. Thus, the western end of Nsadzi Island 

 consists of a high treeless grassy plateau sloping down 

 steeply to a rocky shore along which is a scanty fringe 

 of sparse bushes throwing very little shade over the bare 

 rocks. Yet if one descends to the shore fly is met with, 

 and one is immediately investigated. 



An experiment was made to test whether the fly does 

 roam along this kind of coast. At one point there was 

 a small copse about thirty yards square, furnishing ample 

 shade to provide a base for the fly, and ten fly boys were 

 set to catch flies continuously here on June 10, 1914. 



The fact that the number of males caught per boy per 

 hour was almost unaltered until the end shows that the 

 121 flies could not have been in the copse at the com- 

 mencement, but that a continual influx occurred. Had 

 the flies all been there at first ten boys would soon have 

 diminished the number. Also, after an interval spent 

 in looking for pupae there was a decided increase in the 

 total number of flies caught. 



1 One empty puparium found. 



4 



